Techniques for Battery Quality Control in Production

Author: Glimpse

Poor battery quality can lead to major safety and reliability issues in the field in applications including consumer electronics[1, 2], electric vehicles [3, 4], aviation [5], and more. However, detecting latent cell defects—which are responsible for these battery quality issues—during production is notoriously challenging. In this post, we evaluate the primary techniques used in battery quality control (QC) today.

A summary table of the eleven most common battery QC techniques for full-cell characterization is below. This table was adapted from Table I from the Nature Communications article “Challenges and opportunities for high-quality battery production at scale” [6]. Please refer to the original article [6] for further discussion of battery quality control in manufacturing environments.

Table I: Key requirements of cell-level battery quality inspection techniques. Adapted from Table I from Attia et al. [6]

The table assesses each technique against five critical criteria:​

1. Nondestructive: Can the technique evaluate the cell without destroying it?
2. Scalable to ≤10 s/cell: Is the method fast enough for high-throughput production? If 100% inspection is not possible, is it possible to sample a meaningful number of cells?
3. Full-cell inspection: Does it assess the entire cell rather than regions of interest? This criterion is important since battery defects can occur anywhere in a cell.
4. Spatially resolved: Can it pinpoint the exact location of defects within the cell? This criterion is important to detect latent defects, which have no electrochemical signature until a short-circuit has developed.
5. Resolution of ≤50 µm: Is the technique sensitive enough to detect the electrode-scale defects most often responsible for failure?

Detailed analysis of battery QC techniques

We’ll now evaluate how each method stacks up for battery QC. Overall, we believe that these techniques are more complementary than competitive. In practice, an arsenal of battery QC techniques is the best defence against battery quality issues in the field.

1. Cycling and storage tests

Nearly every battery scientist and engineer is familiar with cycling and storage tests. These are long-term performance tests where cells are cycled (charged/discharged) or left at rest to observe degradation over time. While sampling cells from production for cycling/storage testing is common, this technique has obvious limitations for production-scale QC.

• Pros: The definitive set of techniques to assess performance degradation.
• Cons: Destructive, slow (weeks–years), and not spatially resolved—meaning these techniques can’t identify latent defects until the defects have manifested into failure.

2. Ultra High Precision Coulometry (UHPC)

UHPC is a special category of cycling tests that involves precise measures of charge and discharge efficiency. UHPC provides a sensitive probe of capacity loss and is commonly used in R&D and cell qualification settings to screen new cell designs and electrolyte additives but is not a practical method for QC in production.

• Pros: Highly sensitive to capacity loss, aiding in quantitative forecasting of performance degradation.
• Cons: Destructive, slow (weeks–months), not spatially resolved, and expensive.

3. OCV decay

Perhaps the most standard defect detection test performed in battery manufacturing today is measuring the leakage current during rest after formation [7–9]. This technique can directly capture internal shorting—but not the latent defects that may cause internal shorting in the field.

• Pros: Nondestructive, integrated into existing formation processes, and can directly measure the presence of an internal short.
• Cons: Slow (days–weeks), not spatially resolved, and unable to detect latent defects.

4. Electrochemical Impedance Spectroscopy (EIS)

In EIS experiments, small perturbations are applied to measure an impedance spectrum. This impedance spectrum can be used to quantify the electrochemical health of a battery. EIS is not widely used in battery QC today.

• Pros: Nondestructive and provides unique insights into the electrochemical health of a battery.
• Cons: Expensive, not spatially resolved.

5. High Potential (HiPot) testing

HiPot tests apply a high potential to the cell to measure leakage current and/or internal resistance. HiPot testing is used to detect short circuits due to defects and/or insulation failures and is often used in battery QC.

• Pros: Nondestructive, rapid (~seconds), and can directly measure the presence of an internal short.
• Cons: Not spatially resolved and unable to detect latent defects.​

6. Dissection

During a cell dissection (also known as a teardown), an operator physically opens up a cell to identify material or assembly issues. This technique is often combined with digital photography. While dissection is a standard procedure in battery QC, this method is (obviously) destructive as well as quite labor-intensive and slow.

• Pros: High-resolution, detailed views into internal cell structures.
• Cons: Destructive, labor-intensive, and slow (~hours).​

7. Cross-section

During a cell cross-section, a cell is potted in epoxy, sliced, and imaged via optical microscopy to identify defects, misalignments, or structural inconsistencies. Similar to dissection, cell cross-sections are often performed in battery QC processes, but this method is (obviously) destructive as well as quite labor-intensive and slow.

• Pros: High-resolution, detailed views into internal cell structures and interfaces.
• Cons: Destructive, labor-intensive, slow (~hours), and limited to a maximum of a few 2D planes.​

8. In-line vision systems

In-line vision systems use cameras and software to inspect surface features (e.g., welds, can deformation). In-line vision is widely used in cell production today, but vision is obviously limited to 2D images of the surface of an object.

• Pros: Nondestructive, fast (~100 ms), high-resolution, and effective for surface defect detection.
• Cons: Limited to surface inspections (cannot assess internal defects).​

9. Acoustic testing

Acoustic testing (typically in the ultrasonic frequency range) sends sound waves through the cell and detects internal changes based on wave propagation patterns. Acoustic testing has many advantages, particularly its sensitivity to low-Z components such as electrolyte—making this technique well-suited for evaluating electrolyte wetting. However, one notable limitation is its poor spatial resolution (typically on the order of millimeters).

• Pros: Nondestructive, fast (~seconds to minutes), spatially resolved, and sensitive to low-Z components such as separator and electrolyte.
• Cons: Low resolution (typically ~mm).​

10. 2D X-ray imaging

2D X-ray imaging captures X-ray projections from when X-rays transmit through the battery. 2D X-ray is widely used in battery manufacturing today, mostly for evaluating anode-cathode overhang. While 2D X-ray imaging is nondestructive, fast, and has high spatial resolution, this type of transmission imaging will fail to detect local defects such as metallic particles.

• Pros: Nondestructive, fast (~100 ms), and high-resolution (~10–50 µm).
• Cons: Poor contrast for low-Z components (e.g., lithium, separator) and will miss many defects that require 3D imaging (e.g., metallic particle contaminants).

11. 3D X-ray imaging (computed tomography)

3D X-ray imaging, or computed tomography (CT), uses many 2D X-ray images to create a full 3D view of the cell’s internal structure. CT scanning is often considered to be the “holy grail” battery QC technique as it is capable of nondestructively detecting many cell defects related to geometric structure. While CT scanning is historically a slow technique (~hours), recent advances are driving scan times down to minutes or even seconds.

• Pros: Nondestructive, fast (~seconds with state-of-the-art technology), high-resolution (~10–50 µm), and provides a full 3D view of the cell’s internal structure.
• Cons: Poor contrast for low-Z components (e.g., lithium, separator) and not yet fast enough for 100% inspection.​

A comparison of the last three techniques discussed — acoustic (ultrasound), 2D X-ray, and 3D X-ray — is displayed in Figure 1.

Conclusion

As battery technology continues to evolve, so too must our strategies for ensuring their safety and reliability. This post explored a range of techniques for battery quality control. While no single method offers a perfect solution, we believe high-throughput CT scanning stands out as an especially promising and impactful technique for battery QC.

See also

Computed Tomography Scanning of Battery Cells

About Glimpse

Glimpse is a Boston-based startup pioneering high-throughput CT scanning for battery quality control by solving CT scanning’s two major bottlenecks: scan time and analysis time. First, most high-quality battery CT scans today take an hour or two, which is much too slow for battery quality control. Glimpse has reduced scan time to two minutes using standard CT equipment—and 5-10 seconds using our next-generation CT system—unlocking industry-leading throughput and image quality. Second, CT scanners produce massive quantities of data; each high-resolution CT scan can be dozens of gigabytes each, which makes data analysis slow and labor-intensive. To reduce the analysis time of CT scanning, Glimpse has developed a cutting-edge compute, computer vision, and visualization platform that we call the Glimpse Portal™ (see our free demo here). The Glimpse Portal™ allows battery engineers to understand the quality of their batteries in seconds instead of hours. To learn more, visit https://glimp.se or contact us here.

References

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